bin/ast Add of IR Debugging Features 

Hi,

as discussed with @enebo and subbu I did a the following:
 * moved dot graph generation into own new module `DotGraph`
 * created a new flag -p --pass to only dump ir after -p <pass_name>
 * -h shows which <pass_name>s are available
 * --f, --formatted-ir to print the IR in a concise format
    - indentation for each lexical scope like in the Ruby source code
    - line numbers for IR as in `toStringInstrs()`
    - The scope name is prepended
* -i works as before
* various `require 'jruby'` are merged into a single require in the beginning of the Ruby file